Method of affixing foreing substances to a vitreous body



Oct. '6, 1936. W. WINMNGHOFF 2,056,637

METHOD 0F AFFIXING FOREIGN SUBSTANCES TO A VITREOUS BODY Original FiledJan. 26. 1931 l INVENTQR W WWW ,A Hill 4,/ i l ATTORNEYA Patented oci.6, 1936 UNITED STATES PATENT GFFICE METHOD OF AFFIXING FOREIGN SUB-s'rANcEs To A vrrRnoUs BODY Jersey Application January 26, 1931, SerialNo. 511,409

'Renewed May 14, 1935 15 claims. (ci. sii-7o) The present inventionrelates to the manufacture of vitreous articles, and particularly to theaiiixing of a powdered or granular foreign substance to the walls of avitreous body.

The invention consists in the new and novel method hereinafter set forthand claimed.

A particular object of the invention is to pro- I vide an improvedmethod of producing a vitreous body having a powdered or granularsubstance aiiixed thereto. Other objects and advantages of the inventionwill appear from the following detailed specification or from aninspection of the accompanying drawing.

Considerable difficulty has been'encountered in the past inthemanufacture of various devices having a vitreous envelope to which apowdered or granular foreign substance is affixed. For example, in themanufacture of cathode ray oscillographs, the vitreous envelope of whichmust be coated on the inside with a fluorescent substance such as zincsulphide, willemite, or the like, the various expedients heretoforeemployed to aflix the fluorescent substance to the vitreous envelopehave been long and tedious and at the same time unsatisfactory. Similardiiliculties have likewise been encountered in the manufacture ofmercury vapor arc devices, in which it is often desirable to have agranular substance, such as carborundum, aixed to the cathode bulb incontact with the meniscus of the mercury cathode, in order to facilitatethe startingof the arc. In the latter case, the bulb has commonly beenheated to such a temperature while the carborundum or the like was incontact therewith that the vitreous material partially fused and adheredto the carborundum. This method,`

while the best heretofore known, is Obviously impracticable when theenvelope is of fused silica,

and even when the envelope is'of glass it is notv entirely satisfactory,since the working range between the temperature at which the carborundumwill not adhere to the glass, due to insufficient fusing thereof, andthe temperature at which the carborundum will sink so deeply into theglass as to weaken it physically and electrostatically, due tooverheating thereof, is extremely small; so small, in fact, that bothconditions frequently exist simultaneously-in a single bulb having aconsiderable area exposed to a uniform source of heat, due to thevariations i`n thermal capacity resulting from the variations.

in wall thickness commonly found in blown bulbs. Furthermore, thesoftening of the bulb required to a'ix the granular substance theretotends to produce undesirable distortions in the bulb. The aiiixing ofthe granular substance to appreciable areas of the glass bulb has,therefore, been a serious problem. I have now found that the powdered orgranular substances, such as used in the aforesaid or'similar devices,may 5 be very simply and satisfactorily affixed to a vitreous body by anew method of my invention. According to this new method a thin layer ofa vitreous material having a materially lower softening or fusingtemperature than that'of said 10 body is produced in a suitable manneron that portion of said body to which the foreign substance is to beaffixed. The foreign substance is dusted on, partially embedded in, orintermixed with this layer of vitreous material, as desired, 15 afterWhichsuffcient heat is applied to said body to frit the mass together.In case the material of lower melting point has substantially the samecoefficient of expansion as said body it is, of course, obvious thatthis heating may be con- 2o tinued until complete fusion takes place ifit is so desired. As a result of the lower temperature at which thisprocess may be vcarried out, as compared to that necessary to fuse theforeign substance directlyy to the vitreous body, thedistor- 25 tion ofthe vitreous body which has been lvirtually inescapable with the processheretofore employed is completely eliminated.

For the purpose of illustrating my invention I have shown the apparatuswhich I preferably 3o use to carry out the several steps of my newprocess in the accompanying drawing, in which Fig. l is an elevationalview of the apparatus employed to produce a thin' coatingof a vitreousmaterial having a relatively low melting point 35 on the innersurface ofa vitreous body.

Fig. 2 is an elevational viewl of the apparatus used to partially embedthe foreign substance in said coating, and Y In the practice of myinvention to amx car- .borundum to the interior surface of the cathodebulb' l of a mercury arc lamp of the Cooper 45 Hewitt type I'flrstutilize the apparatus of Fig. 1 to coat the desired portion of theinner/surface of said bulb with the glass of lower melting point. Thisapparatus consists of a bottle 2 having a suitable stopper 3 therein,through which 50 passes a glass tube 4. Air under pressure is suppliedto said tube 4 from any suitable source through the hose 5, a fingervalve 6 which opens into said tube 4 normally affording free escape forsaid air. A restricted orice 1 is also prefer- 55 ably connected to thetube I, particularly when the pressure of said source is appreciable, inorder to reduce the rate yat which the pressure in said bottle 2 isincreased when the nger valve 6 is closed. Said bottle is partiallyfilled with a semi-iluid mixture 8 consisting of ethyl alcohol, or otherreadily volatilizable liquid, in which is suspended particles of a glasssuch as the French seal glass manufactured by Corning Glass Works.Corning, New York, U. S. A., and known to the trade as G858V. Thisglass, which consists of -460% PbO, 5-8% alkali (NazO or KrO) and 33-37% SiOz, has a fusing temperature materially below that of the vleadglass ordinary used for the bulb I, and at the same time has acoeiiicient of expansion which so closely approximates that oi leadglass that it can be fused thereto. Said semifiuid mixture 8 isconveniently prepared by grinding the French seal glass to-an impalpablepowder, such as will pass through a 200 mesh sieve. and then mixing thepowder with4 ethyl alcohol in the proportions of say 500 grams of glassto 250 cubic centimeters of alcohol, the mixture being suicientlyagitated to produce a suspension of the glass particles in said alcohol.The ethyl alcohol employed must, of course, be denatured in orderto'comply with the requirements of the United States Government. Anyapproved denaturant which does not leave a residue which deleteriouslyatl'ects the operation of the lamp or other device being manufacturedmay obviously be utilized for this purpose. A glass tube 9 which passesthrough the stopper 3 terminates at one end below the surface of theglass mixture 8, while the other end connects with a rubber connectionI0, the resilience of which is utilized to provide a liquid tightconnection with a bulb I when the latter is ilrmly held in placethereon, as shown, with the opening II in said bulb I in registry withthe opening in saidconnection Iii.

The apparatus of 2 has'been found to be very convenient for introducingthe carborundllm or the 1ike`int0 the' bulb I. In this Smiths a glasscontainer YIl contains a quantity oi powdered or granular carborundumI6.' The upper end of said container has a glass tube I1 extendingtherefrom, said tube being adapted to extend into the neckof abulbLasshown. A gla'sltube I8 which extends from the lower end of saidcontainer I5 connects with a suitable souroc et air under pressurethrough the hone' Il, a linger valve 20 normally affording substantiallyfree escape 4of air from said hose, suilicient pressure being maintainedin saidhose Il, however, to prevent ilow of the carborundum I tthereinto. ,Y A The coating of powdered glass be fritted or fused to thebulb I in any suitable manner. 1 I preter, however; to usel theapparatus of Fig. 3, which has been found to be very'eilicient and tocause a minimum of glass breakage. This apparatus has 4a. channeled bedplate'v 2i, from opposite ends of. which the rollers 2l are suspended insuch a manner that the endless belt conveyor 21 carried by said rollers28 passes over the top of said bed plate 25, said belt being slowlymoved by suitable propelling apparatus. Attached to said belt conveyorat spaced intervals are a series ot work holding-supports 2l, in theupper end of which the tubular appendages of the bulbs I loosely ilt. Asuitably slotted oven 29 is mounted above said bed plate I in such aposition` that the bulbs I carried by said work holders 28 will passtherethrough as the conveyor 21 progresses Said oven is convenientlyheated by a resistance element lll which is located near the centerthereof, so that there is a temperature gradient from either end of saidoven to a point adjacent to said heating'element 3i. Lateral support forthe work holding supports 2l is provided by the guide members 3| whichare mounted above the bed plate 25, and which extend longitudinally oneither side of the path takenby said supports 28. Said guide members 3ilikewise shield the belt conveyor 21 from the heat which escapes fromthe oven 29 through the opening in the bottom thereof.

In the use and operation oi' this apparatus I first place a bulb I ofglass, quartz, .or any suitable vitreous material, upon the rubberconnection III with the opening Il, to which the negative inlead chamberis sealed at a later stage in the manufacture of the mercury vapor arelamp oi which the bulb I is a part, in registry with the opening in saidconnection. The ilnger valve i is then closed by the operator, causingthe air pressure within the bottle 2 to increase,

the glass mixture 8 being thereby forced upwardly through the tube 8into the bulb I until a pool 8' of said mixture has been formed thereinof desired depth. The pressure is then released by opening the lingervalve 6, whereupon the glass mixture I descends by gravity into thebottle 2, leaving a coating I2 of powdered glass and alcohol of pastyconsistency on the wall of the bulb I. Any excess glass mixture is thenallowed -to drain from the bulb. While the aforesaid coating I2 ofpowdered glass is still moist the tubular portion of the bulb I isplaced over the end oi the glass tube I1, the opening II in said bulbbeing preferably closed, as for example, by the operator's finger. Theiinger valve 20 isthen momentarily closed, forcing the compressedairupward through the mass of granular carborundum Il, some of thiscarborundum being carried with the air through said tube I1 into thebulb I, where it adheres to the moist coating I2 of powdered glass, someof the granules even being partially embedded in saidcoating. 'I'hecoating is then allowed to dry. i

Whenthoroughly dry the coating I2 still adheres to the wall of the glassbulb I sumciently to permit any ordinary handling of said bulb,-althoughany undesired portions of said coating may be easily removed bybrushing or` rubbing.

l In practice it has been found desirable toremove the powdered glassand-carborundum from the area immediately adjacent to the opening II. towhich the negative inlead chamber mustf be later sealed, since thepresence of' the carborundum and the powdered glass coating at um pointtends to make it dimcult to produce a perfect fusion of the parts. Ialso preferably remove enough of the coatingk I2 at one or more pointswhich will be in contact with the mercury meniseus to divide the ringleft around the openingi I, since the carborundum appears to be moreei'iective when the line of contact thereof with said mercury meniscusis discontinuous.

- The bulb I isthen' inserted in a work supporting member 2l which isbeing slowlycarried to- .ward the oven 2l by the belt conveyor 21. Assaid belt conveyor progresses the bulb: I is carried wittdn the oven I,where it is gradually heated as it approaches-the centrally locatedheating element 30, said oven being maintained at such a temperaturethat the French seal glass partially fuses as the bulb I passes saidheating element. seal glass are thereby fritted together and to the Thecarborundum and the French glass of the bulb I, with the result that thecarborundum is firmly and permanently fixed to said bulb. Completefusion of the French seal glass with the glass of the bulb I may beproduced, if desired, although it has not been found necessary. Afterthe bulb I has been carried past the heating element 3D the temperaturethereof gradually falls, due to the temperature gradient in this portionof the oven, with the result that no cooling strains are created in theglass bulb I. After emerging from the oven 29 the bulb I is allowed tocool a little longer, after which it is removed from the work holder 2t.The bulb i is then ready to be fabricated into a mercury arc lamp.y

While I have described a specific method of afflxing the carborundum orother foreign substance to a vitreous surface, other methods arepossible and are -believed to be within the scope of the presentinvention. For example, in some cases the foreign substance may be mixedwith the glass mixture t, and applied to the vitreous surfacetherewith.- This method has, in fact, proved of particular value whensubstances such as willemite are applied to the walls of a cathode rayoscillograph, since it ensures the even distribution. of the substanceover the vitreous surface. It is also useful where a powdered metal,such as aluminum, is to be aiiixed to a vitreous body, such as theenvelope of a gaseous discharge device, particularly a mercury arc lamp.In another variation the glass of lower melting point may be produced bycausing a chemical or physical change in the surface of the vitreousbody to which the foreign substance is to be affixed. For instance, 'ifa lead glass body be coated in a suitable manner with lead oxide andheat applied thereto, a surface coating of a glass richer in lead andhaving a lower melting point than that of the rest of the body will beproduced. This coating may obviously be utilized to affix foreignsubstances to the lead glass body in the same manner as the powderedglassl coating described in detail hereinbefore. be understood,moreover, that various other changes, omissions or substitutions may bemade in the several steps of the process by those skilled in the artwithout departing from the spirit of my invention.

I claim as my invention:

i. The method of alxing a powdered foreign substance to a vitreous bodywhich comprises fritting said foreign substance to said body by means ofa powdered vitreous material having substantially the same coefficientof expansion but a lower fusing temperature than that of said body.

2. The method of afxing a powdered foreign substance to a vitreous bodywhich comprises mixing said .foreign substance with a nely dividedvitreous material having substantially the same coefficient of expansionbut a lower fusing temperature than that of said body, coating thesurface of said body with said mixture, and then heating said mixtureonly to a temperature sufilcient to frit it to said body.

3. The method of alilxing a powdered foreign substance to a vitreousbody which comprises producing a coating on said body of a vitreousmaterial having substantially the same coefficient of expansion but alower fusing temperature than that of said body, dusting, said foreignsubstance onto said coating, and heating said coating only to atemperature sufficient to partially fuse said coating.

It is tov 4. The method of ailixing a powdered foreign substance -to avitreous body which comprises producing a coating of a finely dividedvitreous material having substantially the same coefficient of expansionbut a lower fusing temperature than that of said vitreous body on thatportion of said body to which the foreign substanceis to be affixed,placing said foreign substance in contact with said coating and heatingsaid -coating only to a temperature sufficient to produce a partialfusion thereof whereby' said foreign substance and said coating arefritted to said vitreous body.

5.y The method of afxing a powdered foreign substance to a vitreous bodywhich comprises suspending a quantity of powdered vitreous materialhaving substantially the same coefficient of expansion but a lowerfusing temperature than that of said body in a volatile liquid, applyingthe resulting mass over the surface to which said foreign substance isto be affixed, whereby a moist coating of said vitreous material is lefton said vitreous body, dusting said foregin substance on said moistcoating, and thereafter heating said coating only to a temperaturesumcient to produce a partial fusion thereof where by said foreignsubstance and said coating are fritted to said vitreous body.

6. The method of aiiixing a powdered foreign substance to a vitreousbody which comprises grinding a quantity of a vitreous material havingsubstantially the same coefficient of expansion as said vitreous bodybut a materially lower fusing point than that of said body to animpalpable powder, mixing said powder with a volatiliza'ole liquid,applying said mixture over that portion of said body to which theforeign substance is to be affixed to produce a moist coating of saidpowder thereon, dusting said foreign substance onto said coating, andthereafter heating said coating to frit it to said vitreous body.

7. The method of affixing a powdered foreign substance to a vitreousbody which comprises suspending a quantity of powdered vitreous materialhaving substantially the same coefficient of expansion but a lowerfusing temperature than that of said body in a volatile liquid, applyingthe resulting mass over the surface to which said foreign substance isto-be affixed, whereby a moist coating of said vitreous material isproduced on said body, dusting said foreign substance on said moistcoating, allowing said coating to dry, removing any undesired portionsof said coating, and thereafter heating said coating only to atemperature sufficient to fritsad foreign substance and said coating tosaid vitreous body.

8. The method of aixing a foreign substance to a lead glass body whichcomprises coating a portion of said body with lead oxide, heating saidbody sufliciently to fuse said lead oxide into said body, whereby a. lmhaving a lower melting point than the remainder of said body isproduced, coating said film with particles of said foreign substance,and applying sufficient heat to partially fuse said particles to saidfilm.

9. In combination, a vitreous body, a coating of a vitreous marial onthe surface of said body, said material having a lower fusingtemperature-than said body and a coating of a lforeign substance frittedto the surface of said coatingA of vitreous material.

10. In combination, a vitreous body, a coating of a vitreous material onthe surface of said body, said material having a lower fusingtemperature than said body,

and a coating of a noncoating of vitreous material.

11. An bulb of vitreous material, a coating on the interior surface ofsaid bulb of another vitreous material having a lower fusing point thansaid bulb, and a coating of a granular material fritted to the surfaceof said coating of vitreous material. 12. In combination, a vitreousbody, a coating of a vitreous material on the surface of said body,

4of a vitreous material on the surface of said body,

said material having a lower fusing temperature than said body and acoating of a fluorescent material fritted to the surface o1' saidcoating of vitreous material.

vitreous substance fritted to the surface of said 14. An electricdischarge device comprising a sealed envelope having electrodes sealedtherein for supporting an electric discharge in said device,

a coating of a vitreous material on the inner surface of said envelope,said material having a lower fusing temperature than said envelope, andan exposed layer of fluorescent material fritted to the surface of s aidcoating.

15. An electric gaseous discharge device comprising a sealed envelopehaving electrodes sealed therein, a gaseous atmosphere within saiddevice, a coating of a vitreous material on the inner surface of saidenvelope, said material having a lower fusing temperature than saidenvelope, and.

an exposed layer of iiuorescent material frltted to the surface of saidcoating.

WILFORD J. WINNINGHOFF.

